Engine and exhaust heating

ABSTRACT

A method for controlling a vehicle engine having a plurality of cylinders is provided. The method comprises: during engine idling, advancing spark timing of at least one cylinder to before a peak torque timing, and retarding spark timing from the advanced timing toward the peak torque timing in response to decreased engine speed to maintain idling speed.

FIELD

The present application relates to a system for controlling idle enginespeed control after a cold start.

BACKGROUND AND SUMMARY

An engine of a vehicle can operate in an idle condition duringstationary or other related vehicle conditions. During cold start engineidle conditions, various systems may utilize waste engine heat to hastenengine warm-up, thereby enabling improved emission performance, engineefficiency, etc. As one example, waste exhaust heat may be adjusted tomore rapidly increase catalyst temperature, thereby reducing emissions.Likewise, waste heat in the engine cooling system and/or lubricatingsystem may be directed to the cabin for cabin heating or to thelubricating system, thereby reducing lubricant viscosity thus reducingfriction. For example, spark timing may be retarded from MBT duringinitial starts to first heat an exhaust catalyst, and then once thecatalyst is heated, spark timing may be advanced to before MBT to morerapidly heat engine coolant and/or lubricants to thereby provideincreased engine efficiency.

One approach for adjusting engine operation during cold startingconditions is described in U.S. Pat. No. 6,334,431, which describes amethod for utilizing spark timing advance past minimum spark advance forbest torque (MBT) timing when the engine is under cold start conditionsand after catalyst light-off to heat engine coolant. The advance valueis based on engine coolant temperature, intake air temperature, enginespeed, and manifold absolute pressure. Specifically, at engine speedsbetween 2000-2500 RPM, the spark timing advance is decreased as enginespeed increases, and vice versa. Further, below 2000 RPM, the sparktiming is independent of engine speed.

The inventors herein have recognized problems with the above approaches.As one example, at idling conditions when heating the engine coolant viaadvance timing past MBT, idle speed control may degrade. In particular,if spark timing is further advanced from an advanced timing relative toMBT in response to speed drops, the potential for engine stalls mayincrease. In other words, as spark timing is further advanced past MBT,engine torque decreases. If engine torque decreases too rapidly whilethe engine is decelerating or while entering idle conditions, the enginemay stall.

The above issues are addressed by a method for controlling a vehicleengine having a plurality of cylinder, the method comprising: duringengine idling, advancing spark timing of at least one cylinder to beforea peak torque timing, and retarding spark timing from the advancedtiming toward the peak torque timing in response to decreased enginespeed to maintain idling speed.

By taking advantage of the torque reserve generated by the advancedspark timing used for increasing heat to engine coolant and/orlubricant, it is possible to improve idle speed control under suchconditions. For example, by retarding spark timing in response to a dropin engine speed (while remaining advanced relative to MBT), it ispossible to provide a rapid increase in engine torque, with only minorand likely temporary effects on heat delivered to the engine coolantand/or lubricant. As such, improved idle engine speed control can beachieved with reduced stalls while warming the engine. For example, theabove approach can provide quick-acting torque reserve with the optionof directing waste engine heat to the exhaust or the engine coolant,respectively. In this example, the directional choice of waste heatdelivery can be achieved without impacting the level of torque and whilemaintaining torque reserve.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a direct injection engine with cam actuationsystems.

FIGS. 2A and 2B show movement of the knock limit region as a function ofengine load.

FIG. 3 is a flowchart for selecting an idle speed control mode.

FIG. 4 is a flowchart for controlling transitions between different idlespeed control modes.

FIGS. 5-6 are flowcharts for engine idle speed control for various idlespeed control modes.

FIG. 7 is a chart demonstrating example operation under variousconditions according to one example embodiment.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram showing one cylinder of multi-cylinderengine 10, which may be included in a propulsion system of a vehicle.Engine 10 may be controlled at least partially by a control systemincluding controller 12 and by input from a vehicle operator 132 via aninput device 130. In this example, input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Combustion chamber (cylinder) 30of engine 10 may include combustion chamber walls 32 with piston 36positioned therein. Piston 36 may be coupled to crankshaft 40 so thatreciprocating motion of the piston is translated into rotational motionof the crankshaft. Crankshaft 40 may be coupled to at least one drivewheel of a vehicle via an intermediate transmission system. Further, astarter motor may be coupled to crankshaft 40 via a flywheel to enable astarting operation of engine 10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

In this example, intake valve 52 and exhaust valve 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.The position of intake valve 52 and exhaust valve 54 may be determinedby position sensors 55 and 57, respectively. In alternative embodiments,intake valve 52 and/or exhaust valve 54 may be controlled by electricvalve actuation. For example, cylinder 30 may alternatively include anintake valve controlled via electric valve actuation and an exhaustvalve controlled via cam actuation including CPS and/or VCT systems.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted on theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fueldelivery system (not shown) including a fuel tank, a fuel pump, and afuel rail. In some embodiments, combustion chamber 30 may alternativelyor additionally include a fuel injector arranged in intake passage 42 ina configuration that provides what is known as port injection of fuelinto the intake port upstream of combustion chamber 30.

Intake passage 42 may include a throttle 62 having a throttle plate 64.In this particular example, the position of throttle plate 64 may bevaried by controller 12 via a signal provided to an electric motor oractuator included with throttle 62, a configuration that may be referredto as electronic throttle control (ETC). In this manner, throttle 62 maybe operated to vary the intake air provided to combustion chamber 30among other engine cylinders. The position of throttle plate 64 may beprovided to controller 12 by throttle position signal TP. Intake passage42 may include a mass air flow sensor 120 and a manifold air pressuresensor 122 for providing respective signals MAF and MAP to controller12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof catalytic converter 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. The exhaust system may include light-off catalysts and underbodycatalysts, as well as exhaust manifold, upstream and/or downstreamair-fuel ratio sensors. Converter 70 can include multiple catalystbricks, in one example. In another example, multiple emission controldevices, each with multiple bricks, can be used. Converter 70 can be athree-way type catalyst in one example.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. The controller 12 may receivevarious signals and information from sensors coupled to engine 10, inaddition to those signals previously discussed, including measurement ofinducted mass air flow (MAF) from mass air flow sensor 120; enginecoolant temperature (ECT) from temperature sensor 112 coupled to coolingsleeve 114; a profile ignition pickup signal (PIP) from Hall effectsensor 118 (or other type) coupled to crankshaft 40; throttle position(TP) from a throttle position sensor; and absolute manifold pressuresignal, MAP, from sensor 122. Storage medium read-only memory 106 can beprogrammed with computer readable data representing instructionsexecutable by processor 102 for performing the methods described belowas well as variations thereof. The engine cooling sleeve 114 is coupledto the cabin heating system 9.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

Referring now to FIGS. 2A and 2B, these graphs illustrate example knockconstraints at low and high engine loads, respectively. Each graph showsgenerally how, for a given fuel and air amount in the cylinder, sparktiming affects scaled engine output torque (engine torque over the peakengine torque). Specifically, it shows an example peak torque timing(MBT), with retarded timings relative to MBT on the left, and advancedtimings relative to MBT on the right of MBT. Further, the graphillustrates a range of peak torque timings (MinBT to MaxBT).

As illustrated, engine knock may constrain available spark timing to agreater extent as engine load increases, especially with respect toadvanced timing past MBT. For example, FIG. 2A shows the knockconstraint only at spark timings advanced past approximately 10 degreesof advance past MBT, whereas FIG. 2B shows the knock constraint even at10 degrees retarded from MBT.

FIGS. 2A to 2B illustrate that during light loads, knock constraints mayenable operation at an advanced timing past MBT, at least under someconditions. Light loads may comprise a majority of idling operation, atleast after the initial catalyst warm-up operation, and therefore may beoperated with spark timing advanced past MBT. As such, in variousexamples described herein, such operation may be used to increase heatto the engine coolant and/or engine lubricants to improve performance.

Referring now to FIGS. 3-6, various flowcharts describe exampleoperations of idle speed control. Specifically, during idle conditions,the engine is adjusted to maintain a minimum engine speed even if theoperator is not requesting engine output. For example, an engine controlsystem may adjust engine airflow and/or spark timing to maintain idlingoperation and compensate for disturbances such as actuation of thesteering system, engagement of a climate control air conditioning (A/C)compressor, etc. In engine idle speed control, the control system mayretain a torque reserve, in which it is possible to rapidly increaseengine output to maintain engine idle speed and compensate fordisturbances such as those noted above, via spark timing adjustments.

One mode for maintaining sufficient torque reserve during idlingconditions of the spark ignition engine includes nominally operating atretarded spark timing relative to MBT timing. Such an approach can alsocoordinate with cold starting conditions, in which retarded spark timingis provided to increase exhaust heat provided to an exhaust emissioncontrol device (e.g., catalyst 70) to improve its light-off performance.In this example, the spark timing may be adjusted responsive to enginespeed feedback to enable rapid increases or decreases in engine torqueto maintain accurate idle speed control, while also substantiallymaintaining increased exhaust heat to the catalyst. Specifically, sparktiming may be advanced relative to the nominal spark timing to enable arapid increase in engine torque.

However, once the catalyst has reached light-off temperature, forexample, a second mode may be used in which the engine nominallyoperates at an advanced timing relative to MBT to increase heat rejectedto engine coolant and/or lubricants, and quicker reduction of combustionchamber heat loss as compared to retarded spark timing relative to MBT.Here, the spark timing can also be adjusted responsive to engine speedfeedback to enable rapid increases or decreases in engine torque tomaintain accurate idle engine speed control, while providing excess heatto the cabin at zero fuel cost. However, when operating in this mode,the spark timing can be retarded with respect to the nominal sparktiming to enable a rapid increase in engine speed. For example, if thereis a torque disturbance that reduces engine speed, spark timing can beretarded to increase engine torque and counteract the reduced speed,thereby reducing the likelihood of stalling.

By operating advanced of the peak torque timing, a sufficient torquereserve is maintained for idle speed control while also increasing cabinheating performance.

After delivering sufficient heat to the engine coolant and/or lubricant(e.g., once a desired engine coolant temperature is achieved), theengine may be operated in a third idle mode. In this third mode, sparktiming is retarded relative to the peak torque timing so that asufficient torque reserve is maintained, but with less overall sparkretard from MBT as compared with the first mode. For example, themagnitude of retard relative to the peak torque timing may besubstantially less than that of the first mode so that higher efficiencyof the engine is achieved (e.g., torque output over max torque output).

During idle speed control, transitioning between the above-mentionedmodes involves maintaining the engine torque during the transition;thereafter, the desired spark timing associated with each mode (e.g.,determined by desired catalyst temperature, desired engine coolanttemperature, maintaining engine coolant temperature with sufficienttorque reserve, etc.) may be gradually reached by concurrently adjustingspark timing for the cylinder(s) selected for adjustment and overallairflow (e.g., via adjustment of throttle 62).

Further, the number of cylinders operating with advanced, or retarded,spark timing relative to MBT may be adjusted to one, some, or all of theengine cylinders depending on operating conditions. For example, duringthe first and third modes, all of the cylinders of the engine may beoperated with nominally retarded spark timing, with the timing of all ofthe cylinders adjusted responsive to idle speed control deviations.However, during the second mode, only a subset of the engine cylindersmay be operated with spark timing nominally advanced (and adjustedresponsive to idle speed control deviations), with remaining cylindersoperated with spark timing at MBT (and not adjusted responsive to idlespeed).

FIG. 3 illustrates determination of an idle speed control mode. If it isdetermined that the engine 10 is under cold start conditions (e.g.,engine coolant temperature is approximately equivalent to ambienttemperature) at 310 and the engine is in idle at 312, the routineproceeds to 314 where catalyst temperature is compared to a prescribedthreshold T_(CAT), which may be associated with a catalyst light-offtemperature. Idle conditions may be identified based on vehicle speedbeing below a threshold value and/or based on a release of pedal 72 bythe vehicle operator, for example.

If catalyst temperature is less than T_(CAT), idle speed mode 1 isselected at 316. Mode 1 may operate with a nominal spark timing retardedfrom peak torque timing sufficient to increase exhaust temperature andmore rapidly warm exhaust emission components. As one option, during thecatalyst heating period (e.g., in mode 1), heat flow to the enginecoolant may be reduced so that additional excess heat is directed to thecatalyst.

Further, in mode 1, the spark timing is adjusted about the nominaltiming to control idle speed to a desired idle speed. For example, sparktiming may be advanced relative to the nominal timing (while still beingretarded from peak torque timing) to increase engine output torque andthereby counteract drops in idle speed or to counteract external loadsplaced on the engine. As another example, spark timing may be furtherretarded relative to the nominal timing (while still being retarded frompeak torque timing) to decrease engine output torque and therebycounteract increases in idle speed or to counteract external loadsremoved from the engine. Additionally, throttle adjustments may becoordinated with the spark timing retard and adjustments to maintain thespark timing on average around the nominal timing, while also on averagemaintaining the desired idle speed. Additional details of mode 1 aredescribed in FIG. 5.

If catalyst temperature is at least equal to T_(CAT), it is determinedwhether additional heat of combustion is to be transferred to enginecoolant and/or engine lubricants (e.g., via advancing of spark timingpast peak torque timing). In one example, the routine determines whetheran ambient temperature is less than a determined threshold T_(TH) orvehicle cabin heating is requested by occupants or automated climatecontrol system, and also whether engine coolant temperature is less thana prescribed threshold T_(C) at 320.

If so, the routine continues to 322 to determine whether the engine isin a lower engine idle load region. For example, the routine maydetermine whether engine load (e.g., as determined based on manifoldpressure, engine torque, etc.) is less than a threshold. Further, thethreshold may be based on engine knock limits such that, under lightload conditions, spark timing is also responsive to knock detection.Further still, the magnitude of spark timing advance past peak torquetiming may be limited to reduce encountering knock limitations. In analternate example, the routine may detect a knock threshold.

If the answer to 322 is yes, the routine sets the idle speed controlmode to idle speed mode 2 at 324, further described in FIG. 6, whereinspark timing will be advanced relative to the peak torque timing.Specifically, in one example, mode 2 may include operation with anominal spark timing advanced from peak torque timing sufficient toincrease heat rejected to engine coolant and/or lubricants to morerapidly decrease engine friction, provide cabin heating, reduce exhaustheat flow, etc. Further, in mode 2, the spark timing is adjusted aboutthe nominal timing to control idle speed to a desired idle speed. Forexample, spark timing may be retarded relative to the nominal timing(while still being advanced from peak torque timing) to increase engineoutput torque and thereby counteract drops in idle speed or tocounteract external loads placed on the engine. As another example,spark timing may be further advanced relative to the nominal timing(while still being advanced from peak torque timing) to decrease engineoutput torque and thereby counteract increases in idle speed or tocounteract external loads removed from the engine. Additionally,throttle adjustments may be coordinated with the spark timing advanceand adjustments to maintain the spark timing on average around thenominal timing, while also on average maintaining the desired idlespeed.

If engine load is greater than the predetermined threshold 322, or theanswer to 320 is no, the routine sets the idle speed control mode toidle speed mode 3 at 326. In one example, even when increased heating ofthe engine may be advantageous (e.g., to increase cabin heating), ifsuch operation may result in engine knock or degraded idle speed control(due to insufficient torque reserve as limited by knock), the routineselects mode 3 to maintain sufficient idle speed control. In this way,knock limits may be taken into account and reduced. Further, when engineheating is completed, the routine may also select mode 3 to provide morefuel efficient idling with reduced exhaust or engine heating.

If the engine is not in idle 312, a nominal spark retard is determinedand carried out 318.

In this way, the routine can select among the various idle modes toprovide improved performance under a variety of conditions.

The above example modes may also have various alternativeimplementations. In one example, all cylinders of the engine may beoperated about a nominal timing as set by the various modes. Forexample, in mode 2, each cylinder may be operated about the samenominally advanced spark timing, with each cylinder's spark timing beingadjusted responsive to the current desired and actual engine speedaccording to a control routine, such as a PID controller as describedherein below. However, in another example of operation in mode 2, somecylinders may have a first nominal spark advance, and other cylindersmay have a second nominal spark advance greater (e.g., more advanced)than the first nominal spark advance. In this case, spark timing may beadjusted responsive to differences in the desired and actual speed foronly the cylinders with the second nominal spark advance, whereas thecylinders with the first nominal spark advance may be independent of theidle speed control feedback. Alternatively, even in the case where thecylinders have a different nominal spark advance, all of the cylindersmay be adjusted responsive to idle speed control feedback. In oneparticular example, the second nominal spark advance may be set to asubstantially advanced spark timing such that combustion torque issubstantially reduced such that significant heat can be delivered to theengine coolant and/or lubricating system from those cylinders. Thus, inanother example, some cylinder(s) may have different nominally advancedspark timing and, to modulate engine torque, some cylinder(s) mayfurther advance relative to the nominal spark timing thereby reducingengine torque and other cylinder(s) may retard relative to the nominalspark timing thereby increasing engine torque (while all cylinders arestill advanced relative to MBT).

Likewise, similar modifications can be used in modes 1 and/or 3. Forspark timing adjustments in modes 1 or 3, for example, all cylinders mayundergo the same nominal spark timing retard. Alternatively, allcylinders may be retarded relative to peak torque timing but allcylinders do not have the same spark timing. Still, the spark timings ofeach or a subset of cylinders can be advanced or retarded independentlyto maintain idle speed. In one example, all cylinders may have the samenominally retarded spark timing and each cylinder's spark timing canretard or advance to modulate engine torque. For example, all cylindersmay retard or advance similarly (e.g., with a common magnitude ofchange). In another example, some cylinder(s) may have differentnominally retarded spark timing and, to modulate engine torque, somecylinder(s) may further retard relative to the nominal spark timingthereby reducing engine torque and other cylinder(s) may advancerelative to the nominal spark timing thereby increasing engine torque(while all cylinders are still retarded relative to MBT).

In an alternative embodiment, from a cold start, a portion (e.g., half)of the cylinders may be retarded with respect to MBT and another portion(e.g., half) of the cylinders may be advanced or over-advanced withrespect to MBT to concurrently increase exhaust heat and engine coolanttemperature to provide heat more quickly to the cabin while stillincreasing catalyst temperature. In this case, to maintain idle enginespeed for example, the nominally retarded cylinders may further retardto decrease engine torque and advance to increase engine torque.Further, the nominally advanced cylinders may further retard (whileremaining advanced relative to MBT) to increase engine torque and mayadvance to decrease engine torque. In this case with half of thecylinders retarded with respect to MBT and half of the cylindersadvanced with respect to MBT, to maintain idle engine speed, for examplein response to a drop in idle engine speed, the nominally retardedcylinders may advance (while remaining retarded relative to MBT) toincrease engine speed and the nominally advanced cylinders may retard(while remaining advanced relative to MBT) to increase engine speed.Additionally, the engine may operate with some cylinders advanced andsome retarded during transitions between the various modes describedherein, such as the first, second, and/or third modes.

Further, less than all of the cylinder(s) may be selected for sparktiming adjustment to modulate engine torque while other cylinder(s) maynot modulate engine torque. In one example, half of the cylinders mayhave spark timing at MBT and half of the cylinders may be nominallyretarded. Thus, the idle engine speed responsive cylinders can beadvanced to increase engine torque or retarded to decrease engine torque(while remaining retarded relative to MBT).

It should be appreciated that still further idle speed control modes maybe used, if desired. In the event that the routine selects a mode thatis different than a current operating mode, the engine may transitionbetween the idle speed control modes. FIG. 4 illustrates example controlfor various idle speed mode transitions, once a mode transition has beenidentified.

Specifically, at 410, the routine determines the desired mode asdescribed with regard to FIG. 3. Then, at 412, the routine determines anominal spark timing advance or retard based on operating parameters,including the engine torque produced by the current spark timing. Forexample, if the engine is in mode 1 (retarded spark timing relative toMBT) and is producing a torque TQ and the desired mode is mode 2, theadvanced spark timing relative to MBT that produces TQ is determined asthe new nominal spark timing so that engine torque output is maintainedsubstantially constant while transitioning the spark timing from theretarded to advanced timing. In one example, the routine may transitiona cylinder from the retarded to advanced timing in one cylinder event.

Next, the cylinder(s) to receive the nominal spark timing advance orretard in the new mode are determined at 413, based on, for example,desired time to catalyst light-off or T_(C), engine speed, engine load,engine temperature, etc. As noted above, various cylinders may beoperated with different relative spark timings.

The nominal spark timing is set in the determined cylinder(s) at 414 andthe transition to the new mode is executed at 416. As noted above, thecylinders may be transitioned in a single engine cycle from, forexample, a retarded timing relative to peak torque timing to an advancedtiming relative to peak torque timing. However, by selecting the sparktiming advance at a level producing the same torque as previouslyproduced with retarded timing, a smooth transition may be achieved.Then, if the desired nominal spark advance is different from the advancethat produces constant or the desired torque, the routine may furthergradually adjust spark timing to the desired nominal value whileadjusting throttle to counteract any torque disturbance.

Various example mode transitions and throttle coordination are describedwith regard to FIG. 7, for example.

Referring now to FIG. 5, it illustrates example control for idle speedmodes 1 and 3. First, if mode 1 is determined as the desired mode, anominal spark retard based on the catalyst temperature is determined at510. For example, if the nominal spark retard based on a desired torqueoutput at 412 is greater than the nominal spark retard based on catalysttemperature from 510, the spark timing adjustment may include an advancerelative to the timing selected in 412 to achieve the nominal sparktiming 510. If the nominal spark timing provides sufficient torquereserve as determined at 512, the routine then determines at 514 thecylinder(s), that will undergo spark timing adjustment. In one example,one cylinder may undergo the spark timing adjustment prior to anothercylinder undergoing the spark timing adjustment to smooth the transitionin torque output. Further, in one example, the nominal spark advance isgradually achieved together with a reduction of airflow via throttleopening, so that an abrupt change in engine torque does not occur. Anexample of such operation is described further with regard to FIG. 7.

Returning to FIG. 5, when the nominal spark timing is achieved, desiredidle engine speed N_(O) and actual idle engine speed N_(E) aredetermined and the spark timing adjustment based on these values isdetermined at 522. The desired idle speed may be in a range ofapproximately 500-1300 RPM in one example. Further, in one example, aproportional-integral controller may adjust spark timing responsive tothe difference between the desired idle speed and the actual enginespeed. Further, throttle adjustments may also be coordinated to furthercontrol idle speed, while also maintaining spark timing on average atthe desired nominal value. Further, a feedback gain of the spark timingadjustment may be adjusted according to the number of cylindersundergoing the adjustment, with a higher gain (for greater adjustment)selected when fewer cylinders have spark timing adjusted to maintain adesired idle speed. However, various other control structures may alsobe used.

In one example control routine for idle speed modes 1 and 3, sparktiming is nominally retarded relative to MBT; thus, if actual enginespeed is greater than the desired engine speed as determined at 532, asmay occur if a load is removed from the engine, an adjustment in sparktiming that further retards the timing relative to the peak torquetiming is determined at 534. Alternately, if engine speed is less thanthe desired speed 532, as may occur if power steering is engaged, forexample, a spark timing advance relative to the nominal spark timing isdetermined at 536.

At 524, the cylinder(s) responsive to the speed error are determined.Selection of the cylinder(s) may be based on, for example, magnitude ofspark timing adjustment, engine load, cylinder pressure, etc. One ormore cylinders may undergo the spark timing adjustment, such as notedabove with regard to the various different implementations of the idlespeed control modes. In one example, where spark timing of all of thecylinders is nominally retarded, the timing of each cylinder is adjustedas determined to maintain the desired idle speed. Finally, spark timingcorrections are implemented in the selected cylinder(s) along withairflow changes via throttle opening adjustment at 526 to maintain idlespeed while also maintaining the desired nominal spark timing. In thisway, it is possible to provide desired catalyst heating or sufficienttorque reserve, while also accurately controlling idle speed to thedesired value.

If the nominal spark retard based on catalyst temperature does notprovide sufficient torque reserve 512, a new nominal spark retard,further retarded from peak torque timing, is determined based on thedesired torque reserve at 530 and the routine continues then to 514.

If mode 3 is determined to be the desired mode, a nominal spark retardbased on the desired torque reserve is determined at 528 and the routinecontinues to 514.

Referring now to FIG. 6, it illustrates example control for idle speedmode 2 where cabin heating may be requested or in progress. A nominalspark advance based on the engine coolant temperature is determined at610. For example, if the nominal spark advance based on a desired torqueoutput at 412 is greater than the nominal spark advance based on enginecoolant temperature from 610, the spark timing adjustment may include aretard relative to the timing selected in 412 to achieve the nominalspark timing 610 (along with a corresponding throttle adjustment asdescribed herein).

If the nominal spark timing does not provide sufficient torque reserve,a new nominal spark advance based on desired torque reserve isdetermined at 634. If the nominal spark advance determined at 610provides sufficient torque reserve as determined at 611, the routinethen determines at 612 the cylinder(s) that will undergo spark timingadjustment along with throttle opening adjustment 614. Again, as notedherein, various implementations of the idle speed control modes may beused. In the current example, the nominal spark retard is graduallyachieved together with a reduction of airflow via throttle opening, sothat an abrupt change in engine torque does not occur. For example, onecylinder may undergo the spark timing adjustment prior to anothercylinder undergoing the spark timing adjustment to smooth the transitionin torque output.

Further, in some cylinders, the spark advance may be set significantlyover-advanced such that substantially no positive torque is produced bythose cylinders, and the engine output and speed is maintained by othercylinders (with ignition timing at MBT, retarded from MBT, or advancedfrom MBT). In another example, all of the cylinders may be alternatelyover-advanced such that positive torque is still provided to the vehiclewhile concurrently increasing engine coolant temperature. In stillanother example, some of the cylinders may be over-advanced while othersare advanced but not so overly advanced, such that positive torque isprovided to the engine via the advanced, but not-overly-advancedcylinders, while increasing engine coolant temperature. Further, in yetanother example with some cylinder having a nominal advance past MBT andsome having a nominal retard from MBT, idle speed control can also beachieved with both groups of cylinders, where the advanced cylindersretard spark timing, and the retarded cylinders advanced spark timing,in response to a drop in engine speed. Further, in this example, theadvanced cylinders may be overly advanced so that when idle speed is atthe desired value, they produce substantially no torque, but when theyare retarded toward MBT in response to a speed drop, they producesubstantial positive torque to return the engine to its desired idlespeed. In examples where some cylinders are advanced relative to MBT andsome are retarded relative to MBT, the nominal values for such operationmay be selected to balance cylinder torque among both the advanced andretarded cylinders. Finally, various combinations of the above modes maybe used. For example, overly advanced timing of at least some cylinders,in combination with some cylinders operating at a nominal spark retard,and some cylinders near MBT, both advancing toward MBT of the retardedcylinders and retard to MBT of the overly advanced cylinders may be usedto increase torque in response to a speed drop during idle conditions.

With advanced or over-advanced spark timing, the spark timing advancemay be suspended if maximum cylinder pressure and/or engine knock isdetected. Thus, in one example, the routine may return to no nominalspark advance, or to operation with nominally retarded timing, such asmode 3, for example.

When the nominal spark timing is achieved, desired idle engine speedN_(O) and actual idle engine speed N_(E) are determined and spark timingadjustments based on these values are determined at 620. In one example,a proportional-integral controller may adjust spark timing responsive tothe difference between the desired idle speed and the actual enginespeed. Further, throttle adjustments may also be coordinated to furthercontrol idle speed, while also maintaining spark timing on average atthe desired nominal value. Further still, a feedback gain of the sparktiming adjustment may be adjusted according to the number of cylindersundergoing the adjustment, with a lower gain (for less adjustment)selected when more cylinders have spark timing adjusted to maintain adesired idle speed. However, various other control structures may alsobe used.

In one example control routine for idle speed mode 2, spark timing isnominally advanced relative to MBT; thus, if actual engine speed isgreater than the desired engine speed as determined at 628, as may occurif a load is removed from the engine, an adjustment in spark timing thatfurther advances the timing relative to MBT is determined at 632.Alternately, if engine speed is less than the desired speed 628, as mayoccur if power steering is engaged, for example, a spark timing retardrelative to the nominal spark timing is determined at 632. Thus, thecontrol of engine torque increase and decrease in mode 2 isdirectionally opposite to modes 1 and 3.

At 621, the cylinder(s) responsive to the speed error are determined.Selection of the cylinder(s) may be based on, for example, magnitude ofspark timing adjustment, engine load, cylinder pressure, etc. One ormore cylinders may undergo the spark timing adjustment, such asdescribed above with regard to FIG. 5, for example. In one example,where spark timing of all of the cylinders is nominally advanced, thetiming of each cylinder is adjusted as determined to maintain thedesired idle speed. Finally, spark timing corrections are implemented inthe selected cylinder(s) along with airflow changes via throttle openingadjustment at 622 to maintain idle speed while also maintaining thedesired nominal spark timing. In this way, it is possible to providedesired cabin heating while also accurately controlling idle speed tothe desired value.

Next, it is determined if cylinder pressure has exceeded some thresholdor if there is knocking 623, for example by accelerometers, ionizationsensors or combustion pressure sensors in the cylinder(s). If yes, sparktiming advance is limited and engine airflow is reduced via throttleopening adjustment 624 to maintain the engine speed. Alternately, themode may be switched from mode 2 to modes 1 or 3 (or some other mode notdescribed) wherein the spark timing may be retarded relative to MBT.

In the present application, torque balance may be desirable and thusachieved by setting all cylinders to have substantially similar nominalspark timing or to have spark timing set at one of the two ignitionsettings that produce peak torque (e.g., MinBT and MaxBT in FIG. 2A andFIG. 2B).

A prophetic example of operation during idle operation is described inFIG. 7. Five time diagrams with a common time basis illustrate the sparktiming and throttle opening adjustments as a function of engine speed,engine coolant temperature, and catalyst temperature, among otherparameters.

A cold start is executed at t1, with the engine cranked and spark timingis held at MBT until the engine runs-up and idle conditions are met. Inmode 1, spark timing is nominally retarded relative to MBT untilcatalyst light-off T_(CAT) is met at t3. Thereafter, there is a switchto mode 2 so that spark timing is nominally advanced a magnitude ΔT_(S)relative to the nominal spark timing to maintain the same engine torqueoutput. Disturbances to the system, apparent at t2 and t4, may becaused, for example, by use of the power steering and are controlled byretarding or advancing spark timing relative to the nominal spark timingdependent on mode, as described previously in FIG. 5 and FIG. 6,respectively. Spark timing is subsequently returned to the nominal sparktiming (e.g., t2′ and t4′) after a disturbance with coordination ofadjusting throttle opening and retarding or advancing spark timingdependent on mode. When the desired engine coolant temperature has beenreached, a switch to mode 3 occurs, such that spark timing is retardedrelative to MBT to a nominal value not necessarily equal to that of mode1 such that less excess engine heat can be sent to exhaust outtake andimproved fuel consumption may be achieved. The vehicle may remain inmode 3 while in idle speed control. However, in some examples, evenafter a significant duration of engine or vehicle operation, if thevehicle idles for an extended duration in a significantly cooler ambienttemperature, increased cabin heating may be requested, especially invehicles with large cabin volumes with multiple heating regions. In suchan example, the system may be operated in mode 2 to provide the desiredcabin heating.

Note that in FIG. 7, when there is a switch to mode 2 at t3, the nominalspark advance determined while switching modes is approximatelyequivalent to the nominal spark advance determined by ECT temperature.In this case, further adjustment to the nominal value is not used, ascontrasted with the mode transition at t5.

Note that the example control and estimation routines that are depictedby the above process flows can be used with various engine and/orvehicle system configurations. The specific routines described hereinmay represent one or more of any number of processing strategies such asevent-driven, interrupt-driven, multi-tasking, multi-threading, and thelike. As such, various acts, operations, or functions illustrated may beperformed in the sequence illustrated, in parallel, or in some casesomitted. Likewise, the order of processing is not necessarily requiredto achieve the features and advantages of the example embodimentsdescribed herein, but is provided for ease of illustration anddescription. One or more of the illustrated acts or functions may berepeatedly performed depending on the particular strategy being used.Further, the described acts may graphically represent code to beprogrammed into the computer readable storage medium in the enginecontrol system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and subcombinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for controlling a vehicle engine having a plurality ofcylinders, comprising: during engine idling, advancing spark timing ofat least one cylinder to advanced of a peak torque timing, and retardingspark timing from the advanced timing toward the peak torque timing inresponse to decreased engine speed to maintain idling speed.
 2. Themethod of claim 1 further comprising, during operation with spark timingadvanced from the peak torque timing, further advancing spark timingaway from the peak torque timing in response to increased engine speedto maintain idling speed.
 3. The method of claim 1 further comprisingadjusting spark timing about the advanced timing in response to adifference between a desired idle speed and measured engine speed, wherespark timing is retarded from the advanced timing to increase engineoutput torque responsive to the difference, and advanced from theadvanced timing to decrease engine output torque responsive to thedifference and thereby maintain the desired engine idle speed.
 4. Themethod of claim 3 where the spark timing is set to advanced from thepeak torque timing, and further adjusted about the advanced timing,during cabin heating operation.
 5. The method of claim 3 where the sparktiming is set to advanced from the peak torque timing, and the advancedtiming is adjusted, in response to engine coolant temperature.
 6. Themethod of claim 1 where the spark timing is set to a nominal advancetiming relative to the peak torque timing, said nominal advanceresponsive to engine coolant temperature, where the spark timing isretarded from the nominal timing responsive to idle speed decreasing.7-20. (canceled)
 21. A method for controlling a vehicle engine having aplurality of cylinders, comprising: during engine idling, advancingspark timing of at least one cylinder to advanced of a peak torquetiming, and retarding spark timing of at least one cylinder to retardedfrom a peak torque timing, and retarding spark timing from the advancedtiming toward the peak torque timing and advancing spark timing from theretarded timing toward the peak torque timing in response to decreasedengine speed to maintain idling speed.
 22. The method of claim 21wherein the at least one cylinder has advanced timing substantially pastpeak torque timing such that it produces substantially no output torquewhen at the substantially advanced timing.
 23. A method for controllingan engine having a plurality of cylinders, comprising: maintaining adesired idling speed by: advancing spark timing of a first cylinder toadvanced of a peak torque timing (MBT) while retarding spark timing of asecond cylinder to retarded of MBT; retarding spark timing of the firstcylinder's advanced timing toward MBT and advancing spark timing of thesecond cylinder's retarded timing toward MBT in response to decreasedengine speed.